CVE-2026-9679

ADVISORY - github

Summary

Impact

undici's cookie parser in parseSetCookie percent-decodes cookie values via qsUnescape, turning encoded sequences like %0D%0A, %00, %3B, and %3D into their literal byte equivalents. RFC 6265 §5.4 does not specify any decoding and browsers do not decode either.

Applications that parse a Set-Cookie header and then forward the parsed value into a response header (proxies, middleware, SSR frameworks) become vulnerable to HTTP response header injection: an attacker-controlled upstream can inject arbitrary Set-Cookie, Location, or Cache-Control headers into the application's downstream response, enabling session fixation, open redirect, or cache poisoning.

Affected applications are those that use undici's cookie parsing (parseSetCookie, parseCookie, getSetCookies) and forward the parsed cookie value into a response header.

This was introduced in undici 7.0.0 via #3789.

Patches

Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.

Workarounds

If upgrade is not immediately possible, do not forward values returned by parseSetCookie/parseCookie/getSetCookies directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, ;, and = bytes.

EPSS Score: 0.00205 (0.105)

Common Weakness Enumeration (CWE)

ADVISORY - github

Improper Neutralization of CRLF Sequences ('CRLF Injection')

ADVISORY - redhat

Improper Neutralization of CRLF Sequences ('CRLF Injection')


GitHub

CREATED

UPDATED

EXPLOITABILITY SCORE

2.2

EXPLOITS FOUND
-
COMMON WEAKNESS ENUMERATION (CWE)

CVSS SCORE

5.9medium
PackageTypeOS NameOS VersionAffected RangesFix Versions
undicinpm-->=7.0.0,<7.28.07.28.0
undicinpm--<6.27.06.27.0
undicinpm-->=8.0.0,<8.5.08.5.0

CVSS:3 Severity and metrics

The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.

The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).

A successful attack depends on conditions beyond the attacker's control, requiring investing a measurable amount of effort in research, preparation, or execution against the vulnerable component before a successful attack.

The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.

The vulnerable system can be exploited without interaction from any user.

An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.

There is no loss of confidentiality.

There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any or all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.

There is no impact to availability within the impacted component.

Debian

CREATED

UPDATED

ADVISORY IDCVE-2026-9679
EXPLOITABILITY SCORE

-

EXPLOITS FOUND
-
COMMON WEAKNESS ENUMERATION (CWE)-
RATING UNAVAILABLE FROM ADVISORY

Ubuntu

CREATED

UPDATED

ADVISORY IDCVE-2026-9679
EXPLOITABILITY SCORE

-

EXPLOITS FOUND
-
COMMON WEAKNESS ENUMERATION (CWE)-

CVSS SCORE

N/Amedium

Red Hat

CREATED

UPDATED

ADVISORY IDCVE-2026-9679
EXPLOITABILITY SCORE

2.2

EXPLOITS FOUND
-
COMMON WEAKNESS ENUMERATION (CWE)

CVSS SCORE

5.9medium

Chainguard

CREATED

UPDATED

ADVISORY ID

CGA-6xc8-hw7r-5cqw

EXPLOITABILITY SCORE

-

EXPLOITS FOUND
-
COMMON WEAKNESS ENUMERATION (CWE)-
RATING UNAVAILABLE FROM ADVISORY

minimos

CREATED

UPDATED

ADVISORY ID

MINI-565f-pw9v-hmwp

EXPLOITABILITY SCORE

-

EXPLOITS FOUND
-
COMMON WEAKNESS ENUMERATION (CWE)-
RATING UNAVAILABLE FROM ADVISORY

minimos

CREATED

UPDATED

ADVISORY ID

MINI-67g2-6cpp-6wqg

EXPLOITABILITY SCORE

-

EXPLOITS FOUND
-
COMMON WEAKNESS ENUMERATION (CWE)-
RATING UNAVAILABLE FROM ADVISORY

minimos

CREATED

UPDATED

ADVISORY ID

MINI-v477-cm3p-2wvg

EXPLOITABILITY SCORE

-

EXPLOITS FOUND
-
COMMON WEAKNESS ENUMERATION (CWE)-
RATING UNAVAILABLE FROM ADVISORY